Leukocyte rolling is largely mediated by the selectin family of adhesion molecules. Previous studies have shown severe infections and deficiencies in leukocyte rolling in E- and P-selectin double mutant (E/P) mice indicating the importance of these endothelial selectins in leukocyte recruitment. E/P mice showed no rolling after tissue trauma or 2 hour TNF-α stimulation. Neutrophil accumulation in response to Streptococcus pneumoniae peritonitis was significantly reduced at 4 h., but normal neutrophil accumulation was found at 24 h. This study was conducted to investigate the role L-selectin in leukocyte rolling in venules of the cremaster muscle of E/P mice 6-8 h. after TNF-α stimulation. Hemodynamic parameters were similar in all venules. Rolling flux (rolling cells per min.) was reduced by 88% in E/P mice (9±2) from wild type (wt; 77±17). Rolling in E/P mice was further reduced after 6 h pretreatment with the L-selectin mAb, MEL-14 (1±1 cells/min., 89% reduction). A similar reduction by 67% was seen after acute injection of MEL-14 (3±0.4 cells/min.) in E/P mice. After 6-8 h. TNF-α, wt mice also showed a significant decrease in leukocyte rolling after MEL-14 pretreatment (by 79% to 16±2 cells/min.). A similar low level of rolling was found in L-selectin deficient mice (14±2 cells/min). The L-selectin dependent rolling was sufficient to produce similar levels of adherent leukocytes in E/P (1196±78mm -2) compared to wt (1091±161 mm2)mice. These data provide evidence that leukocyte rolling observed in cremaster venules of E/P mice at 6-8 hrs. after TNF-α is largely L-selectin dependent. This suggests that venular endothelium in vivo expresses potential L-selectin ligand(s) which are sufficient to mediate leukocyte rolling.